As a method for producing a thin film semiconductor device used for IC cards and the like, there is disclosed, in Patent Literature 1, a method for forming a porous layer on the surface of a semiconductor wafer, producing a wafer having a semiconductor film, which is to be an area for forming a device, formed on the surface of the porous layer and forming the thin film semiconductor device by delaminating the wafer along the porous layer after forming the device on the semiconductor film.
According to this method, since the semiconductor wafer is thinned by the delamination, it is not necessary that a back surface side (the opposite side to the surface on the side of forming the device) of the semiconductor wafer after forming the device is removed by grinding, polishing, and the like, unlike a conventional method. As a result, less material loss is incurred, wastes such as cutting chips can be reduced, and thus an environmental advantage can be obtained. Moreover, the number of production wafers to be used can be reduced by reusing the semiconductor wafer after the delamination, and accordingly advantage of the reduction in production cost is greatly expected.
However, when the semiconductor wafer is reused, it is delaminated (separated) along the porous layer, and a minute break or chip is thereby generated on the delaminated surface (separated surface). It is consequently necessary to remove the porous layer having this delaminated surface completely and to form the porous layer again. Therefore, there arises a problem that the thickness of the wafer is thinned by at least an amount corresponding to the thickness of the porous layer whenever the wafer is reclaimed.
In the event that the semiconductor wafer to be reused is thinned whenever the wafer is reclaimed as described above, the whole thickness of the wafer for fabricating the semiconductor device is also thinned. Therefore, when the number of reuse increases, the thickness does not satisfy standard of the whole thickness of the wafer in the device fabrication, and thus the wafer cannot be used in a device fabrication process. There consequently arises a problem that the number of reuse of the wafer is limited.